Recent efforts to recover and characterize dermorphin-like immunoreactive materials (D-LIMs) from the rat duodental tissue have indicated that two categories of D-LIM exist, neither of which is dermorphin. D-LIM A exhibited ion-exchange behavior which resembled that of dermorphin which possesses a blocked C-terminal group and a free N-terminal group. MALDI- TOF analysis indicated a protonated molecular ion of 935 amu which indicates that D-LIM A could be an octa peptide. D-LIM B differed from dermorphin in that it contained an ionizable anionic group. A protonated molecular ion of 1185/1186 amu indicates that D-LIM B could be a nona- or decapeptide. The MALDI-TOF post-source deday mass spectral analysis indicated that D-LIM A is likely to be a peptide which contains proline and tyrosine. Those two amino acids are present in the C-terminal tripeptide sequence [--Tyr-Pro-Ser- amide} of dermorphin which makes up a major portion of the peptide sequence(s) which can be recognized by the antiserum employed to facilitate purification of the D-LIMs. Results of the purification and characterization efforts are consistent with the proposal that D-LIMs A and B are probably peptides which possess structural similarity to the C-terminal amino acid sequence of dermorphin.